Firing circuit for controlled rectifier means



Dec. 16, 1969 A. w. wiLKERsoN 3,484,676

v FIRING CIRCUIT FOR CONTROLLED RECTIFIER MEANS original Filed oct. 21,1965 5 sheets-sheet 1 ATORNEYS Dec. 16, 196.9 A. w. WILKERSON 3,484,676

FIRING CIRCUIT FOR CONTROLLED RECTIFIER MEANS Original Filed Oct. 2l,1965 5 Sheets-Sheet 2 /07 9/ F76, 3 /ga W( O 'QW-* F I' L. "I

l I l j" l I I I i I 1 I I I I s H I Ifa- I I I E I I 77 l I I I 7a I lI y I 96 I I L I I I I I A T J fj 7.3/ "O 9'/ /f/Z y /a 77 /aa I V HG2#aff- I l F/G.7b Q4 f4.5 au I# w 44 I# I INVENTOR ALAN W. WILKERSONATTORNEYS --Dec. 16, 196,9 3,484,676

EIRINC CIRCUIT ECE CCNTECLEED EECTIEIEE MEANS A. W; WILKERSON 5Sheets-Sheet 4 Original Filed Oct. 2l, 1965 l INVENTOR ALAN W WILKERSONwamueu ATTORNEYS Dec. 16, 196.9

FIRING CIRCUIT FOR CONTROLLED RECTIFIER MEANS original Filed oct. 2l,1965 A; wlw-u KERsoN 5 Sheets-Sheet 5 &\ .N.\\\m\ \Il/ IVI is :einer1!||Mi llllllll |1 :1 \w J NNN M \NN l! xm@ @mw m Wam 1w NN v Sw @N r\\Mr www @v MSN i-' vvvv .i L Ii |r||| T o M \mw\ @NN www M \\N`` ALAN W.

4 ATTORNEYS United States Patent O 3,484,676 FIRING CIRCUIT FORCONTROLLED RECTIFIER MEANS Alan W. Wilkerson, Thiensville, Wis.,assignor, by mesne assignments, to Web Press Engineering, Inc., Addison,Ill., a corporation of Illinois Original application Oct. 21, 1965, Ser.No. 499,409, now Patent No. 3,435,316, dated Mar. 25, 1969. Divided andthis application May 13, 1968, Ser. No. 728,634

. Int. Cl. H02m 7/44, 7/ 68 U.S. Cl. 321-47 10 Claims ABSTRACT F THEDISCLOSURE A firing circuit for a controlled rectifier means interposedbetween an alternating current source and an inductive load supplies twofiring pulses during each half cycle of the applied alternating currentvoltage. The first firing pulse causes the controlled rectifier bridgeto energize the load responsive to an input signal. The second pulse,which occurs near the end of each half cycle, provides for a rapidreduction of the inductive energy of the load when the load isde-energized. The provision of the second pulse is independent of theinput signal to the firing circuit.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is adivisional application of cepending application Ser. No. 499,409, filedOct. 21, 1965, now U.S. Patent 3,435,316 issued on Mar. 25, 1969.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to pulse generating circuits and more particularly to pulsegenerating circuits utilizable as ring circuits for controlledrectifiers.

DESCRIPTION OF THE PRIOR ART DC motor braking-general Many applicationsof DC motors require that the motor be braked during operation. Forexample, extremely accurate speed control may require that the motor bebraked as soon as it exceeds a desired speed. Other examples include DCmotors subjected tooverhauling leads, as in crane, hoist, and elevatorservice.

The method and apparatus for controlling such braking action havepresented problems for many years. A simple mechanical brake on themotor output shaft is sometimes employed. While such a device isinexpensive, its braking action is difficult to control. Maintenance ofthe mechanical brake also raises problems. The use of an externalelectro-mechanical brake, such as an eddy current brake, solves some ofthe foregoing problems but, on the whole, external brakes have generallyproven unsatisfactory.

A DC motor may also be braked by adjusting the energization of thearmature and field of the motor. One such method is termed plugging andinvolves reversing the motor armature voltage and current when it isdesired to brake the motor. While the reduction in speed is rapid andthe electrical apparatus required is little and inexpensive, the highcirculating currents in the armature circuit place a large thermalstrain on the motor. Repeated braking operations cannot be performedWithout excessive heating and damage to the motor.

In dynamic braking of a DC motor, a resistor is placed in the armaturecircuit. The motor in effect becomes a DC generator supplying power tothe resistor load. While a ICC resistor limits the armature current andhence the thermal strain on the motor, it also decreases theeffectiveness of the braking action, particularly at low speeds.

Regenerative braking of DC motors also employs the motor as a generator,similar to dynamic braking. However, the vital difference is that inregenerative braking the power generated by the motor is supplied backto the active power source for the motor rather than being circulatedthrough a passive resistor load. Reduced to its essence, power may beregenerated, or supplied back to the active power source for the motor,by reversing the polarity of the armature voltage while maintainingarmature current fiow in the same direction or by reversing armaturecurrent flow while maintaining the polarity of the armature voltage. Ineither case the motor that was formerly a load becomes a power source.The advantages of such a system include the fact that braking may bedone on a permanent basis, whereas plugging and dynamic braking areeffective only in transient conditions or for isolated stops. Also, withproper control, the armature current may be limited, thereby eliminatingthe excessive motor heating experienced with other methods of braking.Braking may also be accomplished very rapidly.

Although alternating current is used as input power to a direct currentmotor control for many reasons, its use is particularly adapted to DCmotor controls providing regenerative braking to the motor. As thevoltage polarity of such an input is continually reversing on a periodicbasis, voltage of either polarity may be supplied to the motor byconnecting the alternating current source to the motor at the propertime.

During motoring operation, the DC motor control rectifies thealternating current input to use half cycles of one polarity of the ACpower to apply a unipolarity voltage to the motor armature. The motorfield is also energized with direct current to cause the motor torotate. The rotation of the armature through the iiux of the motorgenerates a counter opposing the applied voltage. The power controlmeans, such as controlled rectifiers, in the control are arranged to beproperly biased for conduction any time the counter is more negativethan the applied voltage and to supply power from the control as asource to the motor as a load.

During regenerative operation, to cause the motor to become a source forthe control, the motor field is reversed, reversing the motor flux andthe polarity of the counter R.M.F. (assuming the direction of motorrotation remains instantaneously the same). The reverse counter againbiases the controlled rectifiers to conduct current, in the samedirection as during motoring, any time the counter is more negative thanthe applied alternating voltage. This includes portions of the halfcycles of the other polarity, thus permitting the reversal of voltage atthe control terminals necessary for regenerative operation. Aregenerative .DC motor control must therefore provide unidirectionalcurrent in the armature circuit any time the counter of the motor ismore negative than the alternating voltage of the alternating currentpower source. This requires control during all of one half of each cycleof the alternating current input and for a portion of the other halfcycle of that input.

The direction of current How through the motor field and the motor fluxgenerated by the current may be controlled by a controlled rectifiermeans which permits current to ow in either direction through the motorfield.

Prior art regenerative controls have generally dissipated the energy ofthe motor field, during a reversal thereof to initiate regenerativeoperations, in to a resistive network in the field circuit. Thisrequires some finite time for dissipation. During this time, the motoris essentially uncontrolled being in neither the motoring nor theregenerating state, and it is highly desirable to hold such time to aminimum.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide an improved firing circuit for a controlled rectifier meansinterposed between a source and a load, typically an inductive load suchas a motor field. The firing circuit may operate the controlledrectifier means to provide variable energization to the load and it mayfurther operate the controlled rectifier means to rapidly reduce theinductive energy of the load when it is desired to de-energize the load.

The firing circuit may operate the controlled rectifier means to providecurrent in either direction through the load and hence is suitable foruse in the field circuit of a regenerative motor control having acontrolled rectifier means to energize the motor field. Such a ringcircuit reduces to a minimum the time required for reversal of the motorfield.

The firing circuit supplies two firing pulses to the controlledrectifier means during each half cycle of the alternating currentapplied by the source to the load. The instant of applying the firstpulse is proportional to the magnitude of an input signal to the firingcircuit and operates the controlled recifier means to provide variableenergization to the load. The application of the second pulse isindependent of any input signal and occurs whether an input signal ispresent or not. The second pulse occurs in the latter part of each halfcycle and operates the controlled rectifier means to rapidly reduce theinductive energy of the load, as by regenerating the energy back to thesource.

BRIEF DESCRIPTION OF THE DRAWING The specification includes thefollowing drawings, forming a part thereof:

FIGURE l is a schematic diagram of the static, regenerative directcurrent motor control in which the firing circuit of the presentinvention may be employed;

FIGURE 2 is a graph of an alternating current wave form showing theprinciples of motoring and regenerative operation of the control;

FIGURE 3 is a detailed schematic drawing of an operational amplifierwhich may be used in the control of FIGURE l;

FIGURE 4 is a schematic diagram of the controlled rectifier firingcircuit of the present invention which may be used to operate thecontrolled rectifier means in the motor field circuit of the control ofFIGURE l;

FIGURE 5 is a schematic diagram of a controlled rectifier firing circuitwhich may be used to operate the rectifiers of the controlled rectifierbridge in the armature circuit of the control shown in FIGURE l;

FIGURE 6 is a schematic diagram of a current regulating and regenerativelogic circuit which may be used in the control shown in FIGURE 1; and

FIGURE 7a and b are Wave forms illustrating the regenerative operationof the motor field.

DESCRIPTION OF PREFERRED EMBODIMENT Brief description of static,regenerative,

DC motor control In the following specification the static,regenerative, DC motor control is described as one in which the speed ofthe DC motor is regulated. It is to be understood that other operativeconditions of the motor, such as torque, or operative conditions in theapparatus driven by the direct current motor, as for example, webtension, may be the regulated quantity, Hence, the control is not to beconstrued solely as a motor speed control.

Referring now to the drawings, and specifically FIG- URE 1, a blockdiagram of a static, regenerative, DC

motor control 10 is shown therein. Control 10 includes reference andfeedback circuit 14, operational amplifier 16, field circuit 18, andarmature circuit 20. The control drives the DC motor 22 consisting ofarmature 24 and motor field 26 each of which includes or comprisesy anelectromagnetic coil or winding. The control is provided with inputpower from three phase AC lines 28.

Reference and feedback circuit 14 includes a reference signal source 30providing a variable DC signal to conductor 32 by means of DC supply 33and potentiometer 31. A feedback signal is provided by tachometer 34which is connected to armature 24 and supplies a DC signal correspondingto the speed of armature 24 to conductor 36. Conductors 32 and 36 arejoined at mixing junction 38 which provides an error signal to conductor40. The error signal may be of either polarity and serves as a motoringcontrol signal in one polarity and a regenerative braking control signalin the other polarity.

The error signal in conductor 40 is fed to operational amplifier 16which provides a high degree 0f amplification to the error signal. Insubsequent portions of the specification or in ythe claims, thisamplifier may be termed the first amplifier to distinguish it from otheramplifiers in control 10. Amplifier 16 has two output signals, both ofwhich have abrupt saturation points. Both of the signals areproportional in magnitude to the input signal. However, the polarity ofone output signal is the same as the polarity of the input error signalin conductor 40 (termed the direct output signal) -while the otheroutput signal is of the opposite polarity from the input error signal inconductor 40 (termed the inverse output signal). The graph of theseoutput signals forms an X with the direct output signal forming onestroke, and the inverse output signal forming the other `and the twosignals meeting at zero output for operational amplifier 16. One of theoutput signals is used to control both field circuit 18 and armaturecircuit 20 while the other is used to control only armature circuit 20.While FIGURE 1 shows the inverse output signal of operational amplifier16 as being supplied to both field circuit 18 and `anmature circuit 20and the direct output signal of operational amplifier 16 as suppliedthrough conductor 239 to armature circuit 20 only, the connection ofthese output signals may be reversed and the invention is not to beinterpreted aS limited to the connection shown in FIGURE 1. In anyevent, both signals are employed throughout all operational sequences ofcontrol 1-0.

Field circuit 18 includes motor field 26. The field circuit is suppliedwith alternating current from AC supply lines 28 through transformer`42. The output of transformer 42 contains a controlled rectifier meanscomprising two groups of oppositely connected controlled rectifiers 44and 46 and 48 and 50. These rectifiers control the direction of currentflow through motor field 26, one group of rectifiers benig energized foreach direction of current fiow. A field controlled rectifier firingcircuit 52, which may be considered a push-pull proportional firingcircuit, controls the operation of controlled rectifiers 44 through 50in response to the inverse output signal from operational amplifier 16.The control provided by field controlled rectifier firing circuit 52determines which group of controlled rectifiers will be placed in theconductive state and may also include ya determination of the magnitudeofthe field current. Firing circuit 52 also provides for rapid reversalof the current through 'motor field 26 by controlling the operation of-the controlled rectifiers in a manner to regenerate the motor fieldcurrent back to AC supply lines 28.

Filed circuit 18 also contains a resistive network comprising resistors54 and 5-6. These resistors act as a limiting impedance to prevent shortcircuits in the motor field power circuit in the event of faulty firingof the controlled rectifiers and, as a secondary function, reduce thetime constant of motor field 26. Resistors 58 and 71 provide a means ofsensing the polarity of the motor field current.

ing motoring operation and receives power from armature l24 duringregenerative operation. Armature circuit 20 is supplied with powerduring motoring operation from AC `supply lines 28 through transformer60. The amount of power provided to armature 24 is controlled byarmature controlled rectified bridge 62 containing controlled rectifiers-146 through 151. Terminals 306 and 307 constitute the output terminalsof control 10. During regenerative operation power is supplied frommotor armature 24 through armature controlled rectifier bridge 62 andtransformer 60 back to AC supply lines 28.

` A-r-mature controlled recetifier firing circuit 64controls theoperation of the rectifiers in armature controlled rectifier bridge 62.In order to provide reverse voltge capabilities, this firing circuitmust be capable of controlling the operation of the controlledrectifiers through one entire half cycle of alternating current fromsupply lines 28 and through a portion of the other half cycle.

The current regulating and regenerative logic circuit 66 performs a dualfunction. The regenerative logic portion thereof determines whether acombination of conditions in control are proper for the regenerating ormotoring operation and operates armature circuit 20 accordingly. In`making such determination, the logic circuit utilizes a pair of ANDgates operable by a field polarity signal supplied by sensing resistors58 and 71 through conductors 68 and 69 as well as the direct and inverseoutput signals from operational amplifier 16 supplied through conductors238 and 239. The current regulating portion of circuit 66 regulates thearmature current during motoring lor regenerative operation and utilizesan armature current feedback signal supplied by conducto 7l).

DESCRIPTION OF OPERATION OF STATIC REGENERATIVE DC MOTOR CONTROL Theoperation of control 10 may be better understood by initial reference toFIGURE 2 in which the numeral 228 indicates the alternating voltagesupplied to the control through AC supply lines 28. The supply voltage228 includes a positive half cycle 229 and a negative half cycle 230.Only a single phase of alternating current is shown in FIGURE 2 tosimplify the explanation.

As previously mentioned, armature 24 generates a. counter while rotatingin the motoring state. This counter is indicated in FIGURE 2 by thegraph 224 for the motoring operation of control 10. The controlledrectifiers 146, 148, and 150 in armature rectifier vbridge 62 mayconduct any time applied voltage 228 is more positive than counterE.M.F. 224 since, as shown in FIGURE l, the anodes of the controlledrectifiers may be considered connected to AC supply voltage 228 Whilethe cathodes of the rectifiers are connected to the armature and counter224. The controlled rectifiers are properly biased for conductionanytime the anodes are more positive than the cathodes. This is the timeinterval between T1 and T2. The amount of power supplied to armature 24and the speed of the motor 22 during motoring operation is determined bythe point between T1 and T2 at which the rectiers of rectifier bridge 62are rendered conductive. The closer to time T1 the rectifiers arerendered conductive, the greater the supplied power.

During regenerative operation, the energization of motor field 26 isreverse-d, reversing the polarity of the counter of the motor. Thereversed counter E.M.F. is shown by the graph 225 in FIGURE 2. It willbe noted that the time during which the counter E.M.F. of the motor ismore negative than the applied voltage is now much greater, extendingfrom time T5 to time T4. Referring to negative half cycle 230 it willalso be noted that from time T3 to time T4 the voltage on the anodes ofthe controlled rectifiers 146, 148, and 150 in bridge 62, that is,applied alternating voltage 228 has negative polarity with reference tothe AC source.

Since the anodes of the controlled rectifier are more positive than thecathodes thereof, even though they are negative with reference to the ACsource, the controlled rectifiers can conduct current in the samedirection through bridge 62 if a signal is provided from armaturecontrolled re-ctier firing circuit 64. This current will fiow fromarmature 24 through the controlled rectifiers or armature bridge 62 andthrough transformer 60 in regenerative fashion to AC supply lines 28.This is due to the fact that the polarity of the voltage on bridge 62has reversed while the direction of current ow therethrough remains thesame.

It is evident from the foregoing that armature controlled rectifierfiring circuit 64 must be capable of firing the controlled rectifiersboth from time T1 to time T2, for motoring operation, i.e., when thecounter E.M.F. is more negative than the applied AC voltage, and alsobetween time T3 and T4 for regenerative operation, i.e., when theapplied AC voltage has reversed its polarity but before it becomes morenegative than the counter The operation of control 10 in the mannershown graphically in FIGURE 2 is accomplished by employing twooperational loops. These may be termed the inner loop and the outer loopto indicate that the former operates within the confines of the latter.The outer operational loop is utilized to control motor speed andcornprises tachometer 34, operational amplifier 16, current regulatingregenerative logic circuit 66, armature controlled rectifier firingcircuit 64, armature controlled rectifier bridge 62 and armature 24. Theouter loop controls the operation of control 10 as long as operationalamplifier 16 is unsaturated. When operational amplifier 16 saturates,the above described outer loop becomes in operative since further errorsignal changes in conductor 4G are not transmitted through operationalamplifier 16. For normal speed regulating operation, however, theoperational amplier of the outer loop is not saturated and the innerloop serves as an active part of the outer loop.

The inner operational loop is used to regulate armature current at alltimes in accordance with the amplified error signal from amplifier 16.It comprises the armature current feedback signal in conductor 70,current regulating and regenerative logic circuit 66, armaturecontrolled rectifier firing circuit 64, armature controlled rectifierbridge 62, and armature 24. The inner loop is a complete feedbackregulator employing as a reference signal one of the outputs ofamplifier 16, as selected by the logic portion of current regulating andregenerative logic circuit 66, and as feedback, the signal in conductor70. The gain and response of this inner loop regulator are sufficient tocause the armature current to accurately and .rapidly follow the signalfrom amplifier 16, thereby causing the magnitude of armature current tobe proportional to the error signal in conductor 40. However, when theerror signal becomes large enough to saturate the outputs of amplifier16, further increases in error signal can no longer cause an increase inarmature current, since the reference signal to the inner current loopregulator cannot be larger than the saturated output of amplifier 16. Inthis manner the maximum armature current is sharply limited to a valuecorresponding to the saturated output of amplifier 16. One otherconsideration is important. Since the output of amplifier 16 may changealmost instantly from a low level to its highest value the nature ofresponse of the inner loop current regulator to an instantaneous rise inreference signal must include a complete lack of overshoot to prevettransient currents from being larger than the desired maximum value.

The field circuit 18 is operated open loop at or below the base speed ofDC motor 22 except for the field polarity signal in conductor 68 and 69to current regulating and regenerative logic circuit 66. Above the basespeed of DC motor 22, field weakening is required.

To operate control switch 10, switch 72 is closed to energize thecircuitry of the control. Reference signal source 30 is adjusted toprovide a signal corresponding to desired speed. The signal is suppliedthrough conductor 32 to junction 38 and thence to operational amplifier16. Operational amplifier 16 produces a direct output signal and aninverse output signal proportional to the input signal in conductor 4f).As armature 24 is not yet rotating there will be no feedback signalsupplied by tachometer 34.

Field circuit 18 utilizes one of the output signals from operationalamplifier 16 to turn on either rectiers 44 and 46 or rectifiers 48 and50 by means of field controlled rectifier firing circuit 52. The desireddirection of rotation of the motor is determined by which of the twogroups of controlled rectifiers is turned on.

Both the inverse output signal and the direct output signal operationalamplifier 16 are supplied to current regulating and regenerative logiccircuit 66. This circuit determines whether conditions in control areproper for motoring or regenerative operation by means of the polarityof the output signals of operational amplifier 16 and the motor fieldpolarity signals in conductors 68 and 69. These signals operate the pairof AND gates in the logic portion of current regulating and regenerativelogic circuit 66 and operate the armature circuit accordingly. For thepresent motoring operation, the logic portion of current regulating andregenerative logic circuit 66 determines that control 10 is, in fact,capable of such operation and passes the amplified error signal to theinner current regulating loop and thence to armature controlledrectifier firing circuit 64. Armature controlled rectifier firingcircuit 64 provides a firing signal to the controlled rectifier ofarmature controlled rectifier bridge 62 to energize armature 24 andaccelerate the armature.

Acceleration of the armature 24 causes tachometer 34 to generate afeedback signal in conductor 36 which reduces the magnitude of the errorsignal in conductor 40. This likewise reduces the magnitude of bothoutputs of operational amplifier 16 and causes armature controlledrectifier firing circuit 64 to retard the firing angle of the controlledrectifiers in armature controlled rectifier bridge 62. Regulation of thespeed of armature 24 is obtained by controlling the point of firing ofthe controlled rectifiers in armature controlled rectifier bridge 62between time T1 and time T2, as shown in FIGURE 2, by the combinedoperation of the inner and outer operational loops.

Regenerative operation of control 10 may be brought on by reducing thereference signal in conductor 32 or by providing an overhauling load toarmature 24. In either case, the feedback signal generated by tachometer34 in conductor 36 exceeds the reference signal generated by referencesignal source 30 in conductor 32. This reverses the polarity of theerror signal in conductor 40 and hence the polarity of the inverseoutput signal and direct output signal from operational amplifier 16.Because of the high gain of operational amplifier 16 a small reversal inthe polarity of the error signal is sufficient to initiate regenerativeoperation.

The reversed polarity of the output signal from operational amplifier 16to field controlled rectifier firing circuit 52 causes the lattercircuit to energize the other group of controlled rectifiers in fieldcircuit 18 reversing the current through motor field 26. The time ofreversal is short because the inductive energy stored in the winding ofmotor field 26 is regenerated through transformer 42 to AC supply lines28 and because resistors 54 and 56 reduce the time constant of thefield. The reversal of motor field 26 reverses the counter of armature24 and the polarity of the signal in conductors 68 and 69.

Operational amplifier 16 provides output signals of reversed polarity tothe regenerative logic portion of current regulating and regenerativelogic circuit 66. In the absence of the correct motor field polaritysignal from conductors 68 and 69 the logic circuit produces no output atall. The correct signal in conductor 68 or 69, indicating motor fieldhas completed reversal, provides a signal from current regulating andregenerative logic circuit 66 to armature controlled rectifier firingcircuit 64 which controls the point of firing of the controlledrectifiers between time T3 and T4 as shown in FIGURE 2 depending on themagnitude of the error signal in conductor 40. As described inconnection with that figure this operation provides regenerative powerto alternating current supply lines 28.

If the error signal in conductor 40 is excessively large during eithermotoring or regeneration, the operational amplifier 16 becomes saturatedand control over armature circuit conditions is delegated to the innerloop including current regulating portion of current regulating andregenerative logic circuit 66. The current feedback signal is suppliedfrom the armature circuit to the current regulating portion of currentregulating and regenerative logic circuit 66. This circuit alters theoutput signal to armature controlled rectifier firing circuit 64, aftercomparing the feedback signal with a reference signal comprised of thesaturated output of operational amplifier 16, to retard a firing angleof the controlled rectifiers in armature controlled rectifier bridge 62to maintain the armature current at the desired maximum value.

The following comprises the detailed description of the variouscomponents of control 10 shown in FIGURE 1. It is to be understood thatthe invention is not limited to the specific embodiments incorporated inthis detailed description but may utilize equivalent circuits havingsimilar functional characteristics.

DETAILED DESCRIPTION OF OPERATIONAL AMPLIFIER As previously mentioned,this amplifier has a single input and two outputs. Both of the outputsignals are proportional in magnitude to the input signal. However, thepolarity of one output signal is the same as the polarity of the inputsignal while the other output signal is opposite in polarity to theinput signal. The first mentioned output signal has been termed thedirect output signal while the latter signal is termed the inverseoutput signal. The amplifier must, of course, be capable of handlinginput signals from conductor 40 of either polarity.

FIGURE 3 shows a circuit suitable for use as operational amplifier 16 ofcontrol 10. The operational ampli- .fier contains two complementary,three-stage amplifiers.

One such amplifier, 73, is formed of transistors 74, 76 and 78 while theother such amplifier, 75, is formed from transistors 80, 82 and 84. Theinput transistors of each of the aforementioned amplifiers, that is,transistor 74, and transistor are closely matched for identicalcharacteristics, so that the tendency of one such transistor to driftunder operating conditions will be closely matched by the Same tendencyof the other transistor, thereby producing equality in the overalleffect on the two amplifiers.

Amplifiers 73 and 75 are powered by a power supply consisting oftransformer 86, diodes 88, and 89 and capacitors 90 and 91. The powersupply also includes a voltage divider consisting of resistor 92 andresistor 93.

For reasons of overall circuit operation, it is desirable to maintainthe input to input transistors 74 and 80 at zero volts. Thus, a lowimpedance path for the small base current required to establish theoperating points of transistors 74 and 80 is provided by resistors 94and 95 which are joined to the center of the voltage divider network.The voltage divider network provides a small voltage which is used tonull the small voltage drop across resistors 94 and 95 caused by thecurrent.

The input signal from conductor y40 is applied to operational amplifier16 at terminals 96 and 97. A pair of diodes 98 and 99 connected inopposite polarities across input terminals 96 and 97 limit the magnitudeof the input signals to that which can be handled by the operation ofthe amplifier. Specifically, when the magnitude of the input signalexceeds the forward conduction voltage of diodes 98 or 99, the diodesbreak down and short circuit terminals 96 and 97 thereby preventing aninput signal in excess of the breakdown voltage from reaching amplifiers73 or 75. This prevents excessive input signals from overdriving eitherof the amplifiers. Two diodes 98 and 99 are provided to accommodateinput signals of either polarity.

The amplifier utilizes two feedback circuits. The first of thesefeedback circuits may be called the common mode feedback as it affectsboth transistor amplifier 73 and transistor amplifier 75 in an equalmanner. The common mode feedback utilizes resistor 100 which measuresthe sum of the currents through the output of transistors 78 and 84,that is, through the collector and emitter terminals of thosetransistors. The feedback signal comprising the voltage developed acrossresistor 100 is compared with a reference signal generated by a voltagedivider consisting of resistor 101 and a rheostat 102. The error signalbetween the feedback signal from resistor 100 and the reference signalfrom rheostat 102 is supplied through transistor 103 and resistors 104and 105 to the emitters of transistors 74 and 80l to adjust the sum ofthe output of these transistors for any difference between the referencesignal indicating actual total current. Transistor 79 and resistor 77establish the operating point of transistor '3. yIt will be appreciatedthat a high degree of amplification is obtained through transistor 103and the three transistors constituting each transistor amplifier 73 and75 thereby providing rapid, accurate regulation of the sum of the outputof transistors 74 and 80.

The second feedback circuit in operational amplifier 16 is termed thedifferential feedback as it affects differentially amplifiers 73 and 75.This feedback may be resistive, inductive, or capacitive; the characterof the feedback changing the operating characteristics of the amplifierswhich the feedback serves. For example, varying the resistance of thefeedback will vary the amount of gain of the amplifier, while varyingthe capacitance of the feedback will vary the response time of theamplifier. Specifically, in FIGURE 3 a differential feedback is shown byconductor 106 which provides a feedback signal from the emittercollector circuit of transistor 78 through capacitor 107 to inputterminal 97.

The output signals from operational amplifier 16 are supplied toterminals 108 and 109. The direct output signal appears at terminal 108while the inverse output signal appears at terminal 109.

The first mode of operation, called the common mode, is one in which agiven signal or phenomenon affects both transistor amplifiers 73 and 75in an equal manner. Examples of common mode signals or phenomenoninclude variations in line voltage or variations in ambient temperature.As can be readily appreciated, it is necessary that such occurrencesaffect both transistor amplifier 73 and transistor amplifier 75 equallyin order to maintain proper operation of control 10. The second mode ofoperation, termed the differential mode, is one in which a given signalor phenomenon affects one of the transistor amplifiers in a differentmanner than it affects the other transistor amplifier. Examples ofdifferential mode signals include an input signal to terminals 96 and 97or unequal drift of one or the other of transistor amplifiers 73 and 75.

As previously mentioned, the common mode feedback circuit includingresistor 100 and the reference circuit including rheostat 102 insurethat the total current fiowing through output transistors 78 and 84 andtransistor amplifiers 73 and 75 is equal to that established by thereference signal. Thus any changes in the total current due to suchthings as variation in line voltage or in ambient temperature areimmediately corrected by the aforementioned reference and feedbacksignals and the high degree of amplification provided by transistor 103and the three transistors in each of amplifiers 73 and 75.

Operation of operational amplifier 16 in the differential mode to obtainthe aforementioned direct output signal and inverse output signal isobtained by first adjusting operational amplifier 16 so that the signalsat output terminals 108 and 109 are both equal to zero. Once this isaccomplished, variations in the output signal at terminal 109 due to aninput signal to terminals 96 and 97, is accompanied by an equal andopposite change in the output signal at terminal 108, as the totalcurrent through both transistor amplifiers 73 and 75 must remain thesame because of the above described regulation provided by the feedbacksignal from resistor and the reference signal from rheostat 102.

To provide initial adjustment to operational amplifier 16, outputterminal 109 is connected through resistor 81 to input terminal 97.Resistor 81 forms a negative feedback path which tends to reduce theoutput signal at terminal 109 of transistor amplifier 73 to zeropotential with respect to terminal 96. The output signal at terminal 109is brought to exactly zero by adjusting rheostat to alter the currentinput to transistor amplifier 75. Assuming that the output signal atterminal 10-9 is greater than zero, a signal would be applied fromrheostat 110 to the input of transistor amplifier 75 to cause thatamplifier to conduct more heavily. This removes some of the currentfiowing through transistor ampli-fier 73 and reduces the output signalexisting at terminal 109. The reduction in current through transistoramplifier 73 occurs because the total current fiowing through bothtransistor amplifiers 73 and 75 rnnst remain at the value regulated byrheostat 102 and hence an increase in the current flow in one amplifiermust require a decrease in current flow in the other.

After the output signal at terminal 109 has been brought intocoincidence with the Voltage at input terminals 96 and 97, rheostat 102is adjusted to alter the output signal at terminal 108 so that it isalso at zero. Adjustment of rheostat 102, of course, changes the amountof current in the output of the two transistor amplifiers 73 and 75.

However, since the output of transistor amplifier 73 is fixed by thefeedback signal between its output terminal 109 and its input terminals96 and 97, the output of transistor amplifier 75 is varied, thereby toalter the output signal existing at terminal 108. The connection betweenoutput terminal 109 and input terminals 96 and 97 may then be removedand from this time on, an input signal to terminals 96 and 97 producestwo equal output signals of opposite polarity.

It will be appreciated that the three stages of amplification inamplifiers 73 and 75 provide a high gain characteristic to operationalamplifier 16. This allows the amplifier to be extremely sensitive tochanges in the polarity of the error signal in conductor 40 to operatecontrol 10 in the motoring state or the regenerative state as requiredby that signal. The dead band found in prior art controls of this type,in which the control is unable to operate in the correct state, isthereby eliminated.

As a general rule, the output signal at terminal 109, that is, theinverted output signal is connected to field control rectifier firingcircuit 52 and to current regulating and regenerative logic circuit 66.The direct output signal from terminal 108 is also connected to thecurrent regulating and regenerative logic circuit 66. However, it isanticipated that the connections of output terminals 109 and 108 tofield control rectifier firing circuit 52 and to the current regulatingand regenerative logic circuit 66 will be reversed in a considerablenumber of applications of control 10.

DETAILED DESCRIPTION OF MOTOR FIELD CIRCUIT Motor field 26 is energizedby center tap transformer 42 which has the motor field 26 connected inthe center tap thereof. Each end of center tap transformer has onerectifier of two complementary rectifier groups connected thereto.Specifically, controlled rectifiers 44 and 46 conmotor field 26 in onedirection while controlled rectifiers v 48 and 50 constitute the othergroup and conduct current through motor field 26 in the oppositedirection. These rectifiers may be, and are shown in FIGURE 1 as,silicon controlled rectifiers having an anode terminal, a cathodeterminal and a gate terminal. Applying a signal to the gate terminalpermits the rectifier to conduct current or fire, when the anode andcathode terminals are properly biased.

lt will be appreciated that, should one rectifier of each groupaccidentally be turned on simultaneously, a dead short would resultaround a circuit comprising the two controlled rectifiers andtransformer 42. Such short circuiting has been a failing of prior artcontrols of this type as it disables the field circuit. To preventexcessive field current from occurring under such conditions, resistors54 and 56 are included in the motor field circuit to provide a currentlimiting impedance. It will be appreciated that if other means areprovided to protect the motor field circuit from controlled rectifiermislires, current limiting impedences may be eliminated. These resistorsalso reduce the inductive time constant of motor field 26 when it isdesired to reverse the direction of current fiow through the motorfield.

The firing of controlled rectifiers 44 through 50 controlled by thefield controlled rectifier firing circuit of the present invention whichoperates the aforementioned controlled rectifiers to control the amountof current in either direction through the field from zero to maximumand provides for the rapid reversal of the current through motor field26 by regenerating the inductive energy contained therein back to ACsupply line 28. FIGURE 4 shows a field controlled rectier firing circuitwhich may be used as circuit 52 of control 10 shown in FIGURE 1. Firingcircuit 52 is a push-pull proportional amplifier in that it providescontrol to one group of rectifiers for an input signal from operationalamplifier 16 of one polarity and provides control to the other group ofrectifiers for an input signal from operational amplifier 16 of theopposite polarity. In instances wherein it is not desired to control themagnitude of the field current, the firing circuit 52 may havesufficient gain so that a small input signal will drive it full on.

Firing circuit 52 contains two uni-junction firing circuits 114 and 115,each of which controls one of the groups of controlled rectifiers 44through 50 in the motor field circuit in response to an input signalsupplied to terminals 116 and 117. Each of the uni-junction firingcircuits includes a uni-junction transistor 118 and 119 which providesfiring pulses through transistors 120 and 121 to output terminals 122and 123. For example, output terminal 122 may be connected to controlledrectifiers 44 and 46 while output terminal 123 may be connected tocontrolled rectifiers 48 and 50. Transistors 120 and 121 insure that theoutput pulses from uni-junction transistors 118 and 119 are ofsufficient magnitude and duration to fire controlled rectifiers 44through 50.

The aforementioned firing circuits 114 and 11b are provided with a mainenergization circuit, comprised of differential amplifier 124 andalternate energization circuits 125. Differential amplifier 124 isconnected to input terminals 116 and 117. A differential amplifier isused to insure an input operating level near zero and to providebalanced push-pull operation. Each of the inputs is connected to a twostage portion of the differential amplifier 124. Specifically, input 116is connected to input transistor 126 which in turn is connected tooutput transistor 127 while input 117 is connected to input transistor138 and. to output transistor 130. If the input levels to theseterminals is zero, the output from differential amplifier 124 will be ofinsufficient magnitude to turn on output transistors 127 and 130. Thusno energization signal will be supplied to uni-junction transistors 118and 119. If input signals in one polarity or the other are supplied toterminals 116 and 117, either transistor 127 or transistor 130 willbecome conductive. Current flow through the con- V .ductive transistorwill charge either capacitor 131 or capacitor 132 which will supply aninput signal to the respective uni-junction transistor 118 or 119,through diodes 300 and 301 to turn on either controlled rectifiers 44and 46 or controlled rectifiers 48 and 50.

In addition to the aforementioned main energization circuit foruni-junction transistors 118 and 119 there is an alternativeenergization circuit for each of the unijunction transistors which iscompletely independent of any input signal to terminals 116 and 117.These circuits, 125, comprise resistor 327, resistor 328, and capacitor329 and resistor 330, resistor 326 and capacitor 332 respectively. Thevoltage provided by these circuits to the inputs of the uni-junctiontransistors through diodes 133 and 134, respectively, is slightly lessthan that needed to place the uni-junction transistors in the conductivestate. The operation of these circuits will be subsequently explained.

Field controlled rectifier firing circuit 52 is energized from a powersupply comprised of transformer 135, diodes 136, 137, and 302 andcapacitor 303.

Synchronization of field controlled rectifier firing circuit 52 with thealternating current existing in transformer 42 energizing motor field'26 is accomplished by synchronizing circuit 138. synchronizing circuit138 includes resistor 139, resistor 1.40, Zener diode 141 and transistor142. Transistor 142 supplies power across the two base terminals ofuni-junction transistors 118 and 119 and alternate energization circuits125. The period of each half cycle of alternating current input fromsupply lines 28, during which power will be supplied across the baseterminals of un-junction transistors 118 and 119 is determined by thetime interval during which current will fiow through Zener diode 141 andtransistor 142. This interval initiates approximately 10 after thebeginning of the half cycle and terminates approximately 10 before itsend. During this time, a signal supplied from differential amplifier 124will cause one or the other of uni-junction firing circuits 114 and 115to turn on either one of the two groups of controlled rectifiers 44through 50 in the motor field circuit 18. The instant at which thefiring signal is generated is determined by the magnitude of the inputsignal to terminal 116 or terminal 117, an input signal of greatermagnitude tending to generate a firing signal closer to the initialportions of the half cycle of alternating current, thus controlling themagnitude of the field current as Well as its direction.

It is to be noted that since alternating current is applied to thecontrolled rectifiers, a short circuited condition in the field circuitdue to stray firing can exist for only one half cycle of AC. At the end0f the half cycle, the condition will automatically correct itself asthe stray fired rectifier will be biased nonconductive by the appliedAC.

During the time interval that power is supplied to the bases ofunijunction transistors 118 and 119, alternate energization circuitswill have had sufficient time to charge capacitors 329 and 332 throughresistors 327 and 328 and 330 and 326 respectively. However, aspreviously mentioned, the voltages across capacitors 329 and 332 areinsufficient to fire the uni-junction transistors when full input poweris applied across the base terminals thereof. Near the end of the cycle,the voltage applied to the base terminals of uni-junction transistors114 and 115 necessarily becomes less as the end of the half cycle ofalternating current input approaches. Under these conditions of lessenedvoltage across the bases of uni-junction transistors 118 and 119, thevoltage existing across capacitors 329 and 332 becomes sufficient tofire the uni-junction transistors. This generates a firing pulse nearthe end of each half cycle of alternating current. It is to be notedthat the firing signal generated in unijunction transistors 118 and 119by alternate energization circuits 125 is completely independent of anysignal generated in uni-junction transistors 118 and 119 by dif- 13ferential amplifier 124, and occurs even though no input is applied toterminals 116 or 117.

With no input signals to terminals 116 or 117, the firing signals causedby alternative euergization circuits 125 are supplied to all fourrectifiers 44 through 50 of the two complementary groups that -controlthe direction of current fiow through motor field 26. As the firingpulses are supplied to all the rectifiers, the positive voltagegenerated in two of the rectifiers is opposed by the negative voltagegenerated in the other two rectifiers so that the net effect of thevoltage across the motor field is zero.

When an input signal is applied to terminals 116 and 117, the firingpulse generated by alternative energization source 125 has no effect onthe group of rectifiers being controlled by the main energizationcircuit 124 since one of these rectifiers is already conducting and theother is improperly biased for conduction. The firing pulses provided tothe other group of rectifiers by alternative energization source 125generates a current which opposes the current of the conductingrectifier. However, this condition terminates as the applied voltagereverses and the power loss to motor field 26 is of minor significanceas it exists for only of the half cycle.

The firing pulses generated by alternate energization circuits 125 areused to rapidly reduce the current of the motor field to zero byregenerating the inductive energy stored in the field back throughtransformer 42 to AC supply lines 28.

Under normal operation of motor field circuit 18 where, for example,rectifiers 44 and 46 are alternately rendered conductive by fieldcontrolled rectifier firing circuit 52, the graph of the voltage at theright hand terminal of the field is shown by the graph 234 in FIGURE 7a.This is a fully rectified voltage which produces a DC current 235through the field. The conducting rectifier is indicated lbelow eachhalf cycle of graph 234.

If, at some time T1, rectifier 46 is not turned on during theappropriate half cycle, current will continue to flow through the motorfield due to its inductive characteristics. In order to maintain thiscurrent flow the motor field 26 becomes a source whose voltage exceedsthe applied voltage in transformer 42 during the negative half cycle forrectifier 44. Rectifier 44 will continue to conduct during its normalhalf cycle as it is then properly biased for conduction. The graph ofFIGURE 7a subsequent to time T1 shows the field voltage under conditionswhere rectifier 46 is not turned on. It will be noted that, in effect,alternating voltage is applied to the field. This causes the eld currentto decay with a slight ripple to zero at time T2. At this time rectifier44 becomes nonconductive as there is no current therethrough and thevoltage across the field ceases. It may be noted that the decay ofinductive current in the .motor field in the above circumstances is nomore satisfactory than the time constant of the motor field.

It may also be noted that during the time that the motor field may beconsidered a source, the field is regenerating power to alternatingcurrent lines 28, as current is maintained in the same direction throughthe circuit but through the polarity of the source terminals intransformer 42 has reversed. However, during the positive half cycle ofrectifier 44 power is supplied to the field. This supply andregeneration of power results in little net difference and `for allpractical purposes .may be disregarded. Thus, there is no netregeneration or power supply to the motor field and the inductive energyof the field circuit is dissipated in its resistive portion.

In the control of the present invention, rectifiers 44 and 46 are firedon approximately 10 before the end of the half cycle of appliedalternating current voltage by alternate energization means 125 incontrolled rectifier firing circuit 52. The effect of this operation isshown in FIG- URE 7b. As before, a plurality of cycles may be assumed tohave preceded the graph in FIGURE 7b. Also as before, rectifier 44 isfired on but rectifier 46 is not turned on at the appropriate time toconduct current through the motor field from the AC source. This thencauses rectifier 44 to continue to remain on to conduct current from themotor field, as a source, through transformer 42. Approximately 10before the end of the half cycle rectifier 46 is fired on. This turnsoff rectifier 44 as the current now has an alternative path throughrectifier 46 which is preferred since it is in the direction thattransformer 42 desires to provide power to motor field 26. Rectifier 46conducts power to the motor field for the remaining 10 of half cycle. Atthe end of the half cycle, the regenerative operation continues asrectifier 44 is not turned on and rectifier 46 is forced to remain on asthe only path available for current fiow. As the voltage of transformer42 reverses, current is supplied to the positive terminal thereofforming the regenerative action.

For subsequent half cycles, similar operations are performed. This is,rectifier 44 is turned on in the last 10 of the half cycle to regeneratethe inductive energy of the motor field back to power lines 28 when theVoltage of transformer 42 again reverses. The net effect is a very largeregenerative portion of the half cycle and a small power supplyingportion; the power supplying portion being only the final 10 of eachhalf cycle. This rapidly reduces the current in the motor field 26 asshown in FIGURE 7b.

DETAILED DESCRIPTION OF ARMATURE CIRCUIT Motor armature 24 is insertedacross the output terminals of armature controlled rectifier bridge 62of control 10. Armature controlled rectifier bridge 62 comprisescontrolled rectifier 146, 147, 148, 149, 150, and 151 arranged incomplementary pairs and connected in a conventional three phase bridgeconfiguration having output terminals 306 and 307. The three phasesecondary winding of transformer 60 is connected to the input terminalsof armature controlled rectifier bridge 62.

The control of controlled rectiers 146 through 151, both as to whichrectifiers will Conduct and for how long, is controlled by armaturecontrolled rectifier firing circuit 64. As previously mentioned, thisfiring circuit must control the operation of the controlled rectifiersof armature controlled rectifier bridge 62 throughout the entire periodwhen the counter E.M.F. is more negative than the applied alternatingcurrent voltage.

FIGURE 5 shows a firing circuit suitable for use as armature controlledrectifier firing circuit 64. Firing circuit -64 is, in reality, threeseparate firing circuits or amplifiers 264, 364, and 464, each of whichis connected to a complementary pair of controlled rectifiers inarmature controlled rectifier bridge 62 to conduct current fromtransformer 60 through armature controlled rectifier bridge 62 toarmature 24 and back through armature controlled rectifier bridge 62 totransformer 60. The input signal to armature controlled rectifier firingcircuit 64 is supplied to terminals 156 and 157 and input transistors158, 159 and 160. These transistors are connected to the three firingamplifiers 264, 364, and 464. Current feedback from the individualfiring circuits to input transistors 158 through 160 is provided byresistors 161, 162 and 163, and by rheostat 164 and rheostat 1-65. Thesefeedbacks stabilize the input to firing circuits 264, 364 and 464 andalso, by adjustment of rheostats 164 and 165, balance the inputs of thethree individual firing amplifiers.

Firing amplifiers 264, 364 and 464 contain identical circuitry, and forpurposes of explanation only firing amplifier 264 will be explained indetail. It is to be understood that firing amplifiers 364 and 464 areidentical in construction.

Referring now to firing amplifier 264, the output of input transistor158 is supplied through resistor 166 to capacitor 167 which supplies aninput to uni-junction transistor 168. The output from the base terminalsof unijunction transistor 168 is applied to a pair of transistors 169and 170. These transistors form a two-transistor analogy to a siliconcontrolled rectifier. That is, they form a four layer semi-conductorstructure similar to that found in a silicon controlled rectifier. Thecombined operation of transistors 169 and 170 is similar to that of asilicon controlled rectifier and it is to be understood that such acontrolled rectifier may be used if desired. The twotransistor analogyto silicon controlled rectifier operation is explained more thoroughlyin the second edition of the Silicon Controlled Rectifier Manualpublished by the General Electric Company in 1961.

Certain advantages accrue from the use of two-transistors 169 and 170rather than a single silicon controlled rectifier in firing amplifier264. Specifically, the firing current and the holding current may bedetermined by passive elements in the network. The firing current isthat current necessary to place the transistor or SCR in the conductivestate when applied to the base or gate terminal. The holding current isthat current which must pass between the two emitters of the twotransistor configuration or between the anode and cathode of the siliconcontrolled rectifier in order to maintain the device in the conductivestate. In firing amplifier 264 these currents are determined by theresistive network comprised of resistors 171, 172, 173, 174, and 175.Additionally, an extra terminal, that is the collector terminal oftransistor 170, is provided by the two-transistor configuration that isunavailable when a silicon controlled rectifier is used.

The aforementioned collector terminal of transistor 170 is supplied to auni-junction relaxation oscillator comprised of uni-junction transistor176, capacitor 177, resistor 178, resistor 179 and resistor 240. Therate of oscillation of this oscillator is determined by the variouscircuit components connected therewith and is designed to be much fasterthan the rate of pulse generation provided by uni-junction transistor168. It will be appreciated that, when a pulse is generated byuni-junction transistor 168, triggering and retaining transistor 170 inthe conductive state, a signal will be applied from the collector oftransistor 170` to uni-junction transistor 176 and a series of rapidpulses from the base terminals of uni-junction transistor 176 will besupplied to pulse transformed 180 for the remainder of a synchronizationperiod, hereinafter described. The pulses from uni-junction transistor176 are amplified by transistor 181 before being supplied to pulsetransformer 180. Pulse transformer 180 is connected to two controlledrectifiers in armature controlled rectifier bridge 62 by output windings380.

The rapid pulses from uni-junction transistor 176 will be supplied topulse transformer 180 for the remainder of the synchronization perioddetermined by synchronizing circuit 182. Synchronizing circuit 182includes transistor 183, rectifier 184, resistor 185, resistor 186,rectifier 187, and capacitor 188 and serves to synchronize the operationof firing amplifier 264 to the AC supply frequency. synchronizingcircuit 182 is connected between the above described pulse generatingcomponents and a power supply comprised of transformer 189 and diodes190 and 192. The primary of transformer 189 is connected to alternatingcurrent supply lines 28.

At the beginning of each half cycle of alternating current supplied bytransformer 189, transistor 183 will be turned on rapidly by means of asignal supplied through rectifier 187 and resistor 185. Current flowthrough rectifier 187 also charges capacitor 188 so that its lowerterminal is positive. The turning on of transistor 183 provides power tothe remainder of firing amplifier 264 and allows a uni-junctiontransistor 176 to generate rapid pulses to pulse amplifier 180 whentransistor 170 has been turned on by uni-junction transistor 168. Theinstant at which uni-junction transistor 176 begins generating pulses isdetermined by the magnitude of the input signal to terminals 156 and157, input signals of greater magnitude tending to initiate pulse gen-15 erations earlier in the positive half cycle of alternating currentpower.

At the end of the positive half cycle of alternating current, capacitor188 discharges through resistors 186 and 185. This provides a bias tothe base of transistor 183 that allows that transistor to remain on fora portion of the' negative half cycle. When capacitor 188 is discharged,transistor 183 becomes nonconductive, terminating pulse generation byuni-junction transistor 176. The portion of the negative half cycleduring which transistor 183 is conductive depends upon the magnitude ofcapacitor 188. Thus, firing amplifier 264 will initiate pulse generationby unijunction transistor 17 6 in the negative half cycle of alternatingcurrent power for a small input to terminals 156 and 157, i.e., fromtime T3 to T4 in FIGURE 2. As the input signal is increased, theinitiation of pulse generation by uni-junction transistor 176 willadvance from the negative half cycle of alternating current power intothe positive half cycle and may be moved to near the beginning of thepositive half cycle of alternating current. The pulses generated byuni-junction transistor 176 and supplied to pulse transformer 180 tendto place the controlled rectifiers in armature controlled rectifierbridge 62 in the conductive state. The controlled rectifiers willactually begin conducting when they have become properly biased acrossthe anode and the cathode terminals.

By using a plurality of rapid pulses, armature controlled rectifierfiring circuit 64 insures that the controlled rectifiers of armaturecontrolled rectifier bridge 62 will be turned on at the earliestpossible time they become properly biased across the anode and cathode.If the single pulse were employed to render the controlled rectifiersconductive, such pulse might be delivered at a time when the controlledrectifier was improperly biased and, hence, the controlled rectifierwould never be turned on. Thecontrolled rectifiers could also be turnedon by an AC rider or straight DC energization to the gate terminal.However, if signals of this type of sufficient magnitude to insuredependable firing are used, they cause excessive gate dissipation,shortening the life of the controlled rectifier. It will be appreciatedthat, with the plurality of rapid pulses of short duration provided bythe armature controlled rectifier firing circuit 64, excessive gate"dissipation is prevented yet reliable firing is provided, since eachindividual pulse may be of considerable magnitude. Additionally, aspreviously mentioned, armature controlled rectifier firing circuit 64insures that the controlled rectifiers will he turned on as soon as theyare properly biased across their anodes and cathodes.

Current regulating and regenerative logic circuit 66 supplies thecontrol or input signal to armature controlled rectifier circuit 64. Acircuit which may perform the functions of armature current regulationand regenerative logic is shown in FIGURE 6. As its name implies,circuit 66 includes a regenerative logic portion 196 and a currentregulating portion 197. Both the regenerative logic portions 196 and thecurrent regulating portion 197 are energized by a power suply circuitconsisting of transformer 217, rectifiers 218 and 219 and filtercapacitors 220 and 221.

Regenerative logic portion 196 determines whether control 10 is capableof regenerating or motoring on the basis of the polarities of thesignals from operational amplifier 16 and from the motor field viaconductors 68 and 69 and operates the armature circuit 20 accordingly.Regenerative logic portion 196 iscomprised of two AND gates whichrequire the correct combination of signal polarities from the aforesaidsources to produce an output from one of them.

More specifically, regenerative logic portion 196 is comprised of ANDgate 198 and AND gate 199. AND gate 198 consists of transistor 200,connected in emitter follower configuration, and transistor 201, whileAND 17 gate 199 consists of transistor 202, also connected inemitter-follower configuration, and transistor 203. The outputs of ANDgates 198 and 199 are supplied through diodes 204 and 205, respectively,and through rheostat 207 to the input of current regulating portion 197.

The input signals to the regenerative logic AND gate 198 consist of theinverse output signal from operational amplifier 16 applied to inputterminal 213 and the field polarity signal in conductor 68 applied toinput terminal 214. The input signals to the regenerative logic AND gate199 consist of the direct output signal from operational amplifier 16applied to input terminal 215 and the field polarity signal in conductor69 applied to terminal input 216.

For either AND gate 198 or AND gate 199 to open and supply a signal tocurrent regulating portion 197, input signals of the correct polaritymust be present at both input terminals of the AND gate. For example,during motoring operation in one direction, an input signal fromoperational amplifier 16 is supplied to terminal 213 which is of apolarity to lbias transistor 200 into the conductive state. An inputsignal from conductor 68 to terminal 214, indicating the direction ofcurrent fiow in the motor field 26, will be of a polarity to biastransistor 201 off, thereby preventing that transistor from divertingthe output of transistor 200 to conductor 227. This opens AND gate 198and the output of transistor 200 which is proportional to the errorsignal in conductor 40, amplified by operational amplier 16, is suppliedthrough resistor 304 and diode 204 to potentiometer 207 to controlcurrent regulating portion 197 which in turn controls the' operation ofarmature firing circuit 64.

The polarity of the input signal from operational arnplifer 16 toterminal 215 being of the opposite polarity of the signal applied toterminal 213 prevents transistor 202 from conducting and, hence, nosignal can emanate from AND gate 199. Further, transistor 203 is biasedon tending to divert any output from transistor 202 to conductor 227 vWhen control undergoes regenerative operation, the polarities of thesignals from operational amplifier 16 to input terminals 213 and 215reverse as the polarity of the error signal has reversed. This turnsoff' transistor 2001. The reversed polarity of the input signal toterminal 215, however, turns transistor 202 on. The polarity of theinput signals to terminals 214 and 216 does not reverse instantaneouslywhen control 10l initiates regenerative operation as it takes a finitetime 'for the motor field 26 to reverse. During this time no signal willappear from AND gate 198 as transistor 200 is biased off and no signalwill appear from AND gate 199 as transistor 203 diverts the output oftransistor 202 since the polarity of the signal in conductor 69 appliedto terminal 216 has not yet reversed.

When the direction of current flow through the motor field 26 doesreverse, indicating the motor field is now ready for regenerativeoperation, the polarity of the signal in conductor 69 reverses. Thisturns off transistor 203 and opens AND gate 199 to provide a controlsignal through diode 205 to junction 206 which acts as a control signalduring regenerative operation of the control.

Operation in the other direction of motor rotation is the opposite ofthe above described operation.

Current regulating portion 197 of current regulating and regenerativelogic circuit 66 consists of a two stage amplifier with the associatedinput, feedback, and output circuits. The first of the amplifierconsists of transistors 208 and 209 and is a differential stage. Thetotal current through both transistors 208 and 209 is determined by theIsupply voltage across capacitor 221 and the value of resistor 222. Avariation in the emitter collector current of transistor 208 provides anequal but opposite variation to the emitter collector current oftransistor 209` in order to maintain the total current constant. Thisvariation is applied to the base of transistor 210 forming the secondstage of the amplifier. The output of the emitter collector circuit oftransistor 210 is applied to output terminal 212.

The inputs to current regulating circuit 197 consist of the signal fromthe regenerative logic circuit 196 applied to potentiometer 207 and asignal proportional to armature current supplied to input terminal 211.The magnitude of the signal applied to junction 223 from regenerativelogic circuit 196 is controlled by potentiometer 207 and the magnitudeof the output signals of operational amplifier 16. This signal is thenmixed With the current feedback signal at junction 223 to form an errorsignal which is supplied to the base of transistor 208. As the currentfeedback signal is a series of current pulses, the error signal isfiltered through capacitor 230 and resistor 231.

A compensating feedback is also provided in current regulating portion196. This is a negative feedback from the output of transistor 210 tothe input of transistor 208 and is passed through capacitor 232 andresistor 233. This feedback alters the time response of the amplifier toprevent overshoot and to insure stable, balanced firing of armaturecontrolled rectifier bridge 62. The compensating feedback must be of asufficient magnitude so that there is no overshoot under the most severeinput signal conditions.

The output signal is supplied to terminal 212. This output signal isinverted with respect to the input signal. Specifically, because of thedifferential configuration of transistors 208 and 209, an increase inthe signal to the base of transistor 208 increases the output of thattransistor while decreasing the output of transistor 209 since the totalcurrent flow through both of them must be constarrt. The decrease inoutput of transistor 209 is amplified by transistor 210 and supplied tooutput terminal 212. The reason for inverting the output signal is tosimplify obtaining the negative feedback signal required for thecompensating feedback. The polarity of the output from circuit 66 isarranged so that an increased error results in an increased or advancedfiring angle to the controlled recifiers in bridge 62.

The operation of the current regulating portion 197 of currentregulating and regenerative circuit 66 is critical to the overalloperation of control 10 as portion 197 operates the previously describedinner current regulating loop of the control. This inner loop is a trueregulating circuit with lboth reference and feedback signals and is ofhigh gain so that only a small error signal between the reference andthe feedback is sufficient to produce maximum output.

, Because of the true regulating action of current regulation portion197, the armature current is maintained at all times proportional to thereference signal from potentiometer 207, which is in turn proportionalto the output signals of operational amplifier 16, except when the ANDgates 198 and 199 of regenerative logic circuit 196 are not open.

Current limiting action of the inner current regulating loop occurs whenthe input signals to operational amplifier 16 are of sufiicientmagnitude to cause saturation of its output. When the output ofoperational amplifier 16 becomes saturated, a limit is reached in themagnitude of signal that can be delivered through either AND gate 198 or199 and potentiometer 207. Since the signal through the potentiometer207 is the reference to current regulating portion 197, a limit is alsoplaced on the amount of armature current that the inner currentregulating loop will allow. This action provides the aforementionedsharp current limit. It will also be noted that the current limit actionis obtained without the necessity of transiently excessive armaturecurrent to trigger the limiting means.

The compensating feedback through capacitor 232 and resistor 233 aroundcurrent regulating portion 197 modifies its response to preventovershoot of armature current under the most abrupt saturation ofoperational amplifier 16.

A- full appreciation of the relationship and interaction 19 of thedetailed elements of the above described components in the structure andoperation of the control may be had by referral to the foregoingDescription of Operation of Static Regenerative DC Motor Control andreference is hereby made to that portion of the specification.

While the present embodiment of the invention is considered preferred,it is appreciated that numerous modifications may be made to the presentinvention.

I claim:

1. A controlled rectifier firing circuit (52) for operating a controlledrectifier -Ineans (44, 46 or 48, 50) responsive to an input signal tothe firing circuit, said controlled rectifier means being connectedbetween an alternating current power supply (42) and an inductive load(26) for conducting successive half cycles of the alternating currentthrough the load to provide a unidirectional load current, said firingcircuit comprising: a pulse generating means (114 or 115) coupled to thecontrolled rectifier means and having an operative state synchronized tothe half cycles of alternating current, said pulse generating meansbeing energizable when in the operative state for generating firingpulses to the controlled rectifier means during the half cycles ofalternating current; a first energization means (124) operativelyconnected with said pulse generating means for energizing the latterresponsive to the input signal to cause said controlled rectifier meansto successively conduct at least portions of the half cycles ofalternating current through the load; and an alternative energizationmeans (125) operatively connected with said pulse generating means, saidalternative energization means being coupled to the alternating currentpower supply and responsive to the half cycles thereof for energizingsaid pulse generating means to generate firing pulses near the ends ofthe half cycles of the alternating current to provide a conduction pathin the controlled rectifier means between the load and the power supplyfor the inductive energy of the load.

2. The controlled rectifier firing circuit of claim 1 including asynchronizing circuit (138) connected to the alternative energizationmeans to energize the pulse generating means for biasing said pulsegenerating means into the operative state during the half cycles ofalternating current.

3. The controlled rectifier firing circuit of claim 2 wherein saidalternative energization means is coupled to the alternating currentpower supply through said synchronizing circuit.

4. The controlled rectifier firing circuit of claim 3 wherein saidsynchronizing circuit includes a Zener diode (141) interposed betweenthe alternating current power supply and said pulse generating means andalternative energization means for biasing said pulse generating meansinto the operative state during periods when the voltage magnitude ofthe half cycles of alternating exceeds the breakover voltage of saiddiode and for causing said alternative energization means to energizethe pulse generating means at the end of said periods.

5. The controlled rectifier firing circuit of claim 1 wherein said firstenergization means comprises an amplifier (126-130) having inputterminals (116 and 118) responsive to the input signal and an outputterminal connected to said pulse generating means and said pulsegenerating means includes a uni-junction transistor (118, 119) havingits input connected to said amplifier output terminal and its outputcoupled to said controlled rectifier means.

6. The controlled rectifier firing circuit of claim 1 for operating acontrolled rectifier means (44, 46, 48 and 50) responsive to abipolarity input signal to the firing circuit, said controlled rectifiermeans being connected between the alternating current power source andthe inductive load for conducting successive half cycles in eitherdirection through the load, said control rectifier firing circuitincluding a pair of pulse generating means coupled to the controlledrectifier means, Said pulse generating means each having an operativestate synchronized to the half cycles of alternating current and beingenergizable when in the operative state for generating firing pulses,one of said pulse `generating means (114) generating firing pulses tothe controlled rectifier means, when energized, for causing thecontrolled rectifier means to conduct at least portions of the halfcycles in one direction through the load, the other of the pulsegenerating means (115) generating firing pulses to the controlledrectifier means, when energized, for causing the controlled rectifiermeans to conduct at least portions of `the half cycles in the otherdirection through the load, said first energization means (124) beingresponsive to the polarity of the input signal for energizing one ofsaid pulse generating means responsive to an input signal of onepolarity, said first energization means energizing the other of saidpulse generating means responsive to an input signal of the otherpolarity, said alternative energization means (125) energizing saidpulse generating circuits to produce pulses near the ends of the halfcycles of the alternating current to provide a conduction path in thecontrolled rectifier means between the load and the power supply toregenerate the inductive energy of the load to the power supply during adecrease in the current through the load.

7. The controlled rectifier firing circuit of claim 6 wherein said firstenergization means comprises a differential amplifier (126-130) havinginput terminals (116 and 117) responsive to the input signal and outputterminals connected to said pulse generating means, said pulsegenerating means including uni-junction transistors (118 and 119) havingtheir inputs connected to said amplifier output terminals and theiroutputs coupled to said controlled rectifier means.

8. The controlled rectifier firing circuit of claim 6 wherein saidalternative energization means comprises an alternative energizationcircuit operatively connected with each of said pulse generating means.

9. The controlled rectifier firing circuit of claim 6 including asynchronizing circuit (138) connected to the alternating current powersupply and to said pulse generating means for biasing said pulsegenerating means into the operative state during the half cycles of thealternating current of the supply.

10. The controlled rectifier firing circuit of claim 9 wherein saidalternative energization means is coupled to said alternating currentpower supply through said synchronizing circuit and wherein saidsynchronizing circuit includes a Zener diode 141) interposed between thealternating current power supply and said pulse generating means andalternative energization means for biasing said pulse generating meansinto the operative state during periods when the voltage magnitude ofthe half cycles of alternating current exceeds the breakover voltage ofsaid diodes and for causing said alternative energization means toenergize the pulse generating means at the end of said periods.

References Cited UNITED STATES PATENTS 3,281,645 10/1966 Spink 307-252 X3,304,486 2/1967 Michaels 307-252 X 3,319,147 5/1967 Mapham 307-252 X3,349,312 10/1967 Bergman 321-5 3,395,334 7/1968 Stein 323-22 3,399,3378/1968 Stone 321-5 LEE T. HIX, Primary Examiner W. H. BEHA, AssistantExaminer U.S. Cl. X.R.

